The statements in this section merely provide background information related to the present invention and may not constitute prior art.
Technologies for compressing video data include H.261, H.263, H.264, MPEG-2, MPEG-4, and so on. According to such video compression standards, each image is divided and encoded into fixedly sized macroblocks formed of rectangular areas having pixels sized 16×16 of luma component and pixels sized 8×8 of chroma component. All luma components and all chroma components of each macroblock are spatially or temporally predicted, and then a predicted residual undergoes a transform, a quantization, and an entropy coding and finally a transmission.
The most recently enacted H.264/AVC standard prescribes an encoding apparatus to use a 16×16 pixel block for the fixed macroblock size and subdivide each macroblock into smaller blocks for which an intra prediction or an inter prediction is carried out. In carrying out the intra prediction encoding, each macroblock may be divided into 16×16, 8×8, or 4×4 sizes, and the block of size 16×16 is intra predicted in one of four prediction modes, 8×8 and 4×4 blocks are intra predicted in one of nine prediction modes. In the case of inter prediction, the macroblock may be subdivided into blocks of sizes 16×16, 16×8, 8×16, 8×8, 8×4, 4×8, or 4×4, and then used for the inter prediction through a motion compensation. The transform is performed in the unit of 8×8 or 4×4 sized blocks, and the quantization used for the transform coefficients is scalar quantization.
However, the 16×16 macroblock may be considered appropriate for small images by the class of the conventional QCIF (Quarter Common Intermediate Format) and CIF (Common Intermediate Format) and it is not the right macroblock size for compressing a high resolution image such as a 4K×2K image. In addition, since typical video compression technology uses a fixedly sized macroblock in encoding an image (even though H.264/AVC subdivides and encodes macroblock into smaller block units, the macroblock is of a fixed size), encoding the high resolution image hardly achieves a sufficient encoding efficiency.